1. Field of the Invention
This invention has to do with mechanically actuated disc brake systems and more particularly, methods and apparatus for returning an actuating piston thereof to an initial position.
2. Description of the Prior Art
Retraction of the brake piston to its original position is of primary importance in this invention.
Many disc brake systems are known where the purpose of a retraction system is to move a caliper piston and its associated friction pad away from the brake rotor when the brake is disengaged. The prior art known to the applicant also performs a second function that is not desired or beneficial in the applicant's embodiment. This second function is to provide adjustability in the brake piston arrangement so that the friction pad is always close to (but not touching) the brake rotor thus minimizing the stroke necessary to apply the brakes. The applicant proposes that this "wear take-up" feature in the prior art is not necessary with the instant invention and would actually be detrimental to the efficiency of this disc brake unit.
In a hydraulically actuated disc brake system the piston usually accommodates a sealing ring of generally square cross section. The sealing ring primarily seals the piston-to-cylinder clearance preventing fluid from leaking out of the fluid chamber. Several U.S. patents have issued wherein the sealing ring also has resilient properties that tend to slightly retract the fluid actuated piston in the bore. None of these devices prevent the piston from moving laterally in the bore as the function pad wears out. This lateral motion is welcomed in the prior art as it allows the wear take-up provision but this is not desired in the instant invention as the primary purpose is to retract the piston to an unadjusted permanent position.
Also a problem with prior art devices, where the piston is a sliding fit in the host bore, is that when these adjacent surfaces are exposed to dirt, water and mud corrosive problems could exist and cause these parts to seize.